I do need help.
Sorry for my poor English
Here is what i've done and happened to my kindle touch.
I upgraded my kindle from 5.03 to 5.1, but it bricked.
so i downgraded it back to 5.0,and made it to 5.1 successfully.Since I'm a Chinese ,I tried to change the fonts without jailbreak(by using simple_usbnet_1.1,it said that updated successfuly,but still bricked), sadly it failed.
So I thought about upgradeing to 5.03 , unfortunately it bricked again!!!
Then I hoped to downgrade it back to 5.0.
After D)exit ,reboot or Disable Diags--->D)--->Q) ,the kindle stuck at "System diags".